Phase and frequency modulation



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G.L;USSELMAN PHASE AND FREQUENCY MODULATION Filed June'8, 1932 2 Sheets-Sheet l ach EL 3- G, L.. USSELMAN @3535 PHASE AND FREQUENCY MOJULATION Filed June 8, 1932 2 Sheets-Sheet 2 INVENTOR GEORGE L. USSELMN x ATTORNEY Patented Mar. 31, 1936 UNITED STATES PATENT PHASE AND FREQUENCY MODULATION George L. Usselman, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application June 8, 1932, Serial No. 616,026

7 Claims. (Cl. Z50- 17) This invention relates to signalling means and utmost importance since one of the main drawin particular to means whereby the characterisbacks to signalling is the effect of fading of tics of high frequency oscillations, other than the the transmitted oscillations. Especially is this amplitude, are varied in accordance with signals method desirable now since it is adaptable Where to be transmitted. diversity reception methods are not in use. 5

It' has been found that ordinary amplitude The present invention relates to a new and modulated high frequency oscillations in transnovel method of and means for producing high mission from the sending station to the receivfrequency oscillations, phase and/or frequency ing station are subject to what is known as fading modulating the same, and transmitting the re- 10 effects. This is a decided disadvantage since it sultant energy. l0

introduces drop outs and errors in the signal. More in detail, the object of the present in- Even where diversity receivers are used to receive vention is to provide a new method of and means the amplitude modulated signals the effect of for producing high frequency oscillations and fading is a serious disadvantage. phase or frequency modulating the same in a I have found that if the high frequency osoilnovel manner with modulating oscillations or l5 lations are modulated in phase or in frequency voice frequency modulations obtained from a in accordance with the signal to be transmitted novel thermionic tube arrangement which, by a they are less subject tol the effect o-f fading than single switching operation, may be made to operamplitude modulated waves. The reason why ate as a modulating frequency oscillation generphase or frequency modulated oscillations in teleator, or as an amplifier for the voice frequencies, 20 graph transmission are subject to a less extent with which the high frequency oscillations are to fading effects is that this type of modulation to be phase or frequency modulated. The moduproduces a larger number of side frequencies than lating frequency oscillations generated by this that produced by amplitude modulation, and the novel tube arrangement and the amplified voice result in receiving a phase or frequency modufrequency potentials, whichever is used for modu- 25 lated signal on a simple receiving antenna is very lating the high frequency oscillations, are passed similar to receiving an unmodulated signal on through a symmetrical thermionic stage which adiversity antenna. Aphase or frequency moduaffects the modulation in phase or frequency lated signal is of particular advantage for reducof the high frequency oscillations generated.

ing fading when simple receiving antennas are An apparent advantage to be gained by the 30 used and this type of modulated signal is also use of the present novel method of and means for beneficial for reducing the effects of fading when phase or frequency modulating high frequency diversity receiving systems are used. oscillations is that increased efficiency in opera- Phase and frequency modulated high frequency tion is obtained and that the range and traffic oscillations have many characteristics in common, speed of the transmitter of a given power has as will appear more in detail hereinafter. If high been greatly increased.

frequency oscillations are phase or frequency Another advantage arising from the use of the modulated by a single modulating frequency they present invention is that the thermionic tube used are physically indistinguishable. At least, at the to produce the modulating oscillations may, by

4U present time, with the present analyzing means, a mere reversal of position o-f a switch, be used 40 this is true. When a band of modulating freas an amplifier for the voice frequency oscillaquencies is used it may be shown that in phase tions so that the phase or frequency modulated modulation all modulating frequencies of equal transmitter may be used either for code signalling amplitude have equal eect upon the carrier or for voice frequencies without the use of ad- 35 phase, Whereas in frequency modulation the effect ditional tubes. 45 upon the phase of the carrier ls inversely pro- In addition to the above, it is noted that the portional tothe modulating frequency. However, present phase or frequency modulated transwhere a band of modulating frequencies is applied mitter is admirably adapted for use with receivto the high frequency oscillations ln phase moduing systems without diversity reception and, since lation, the phase of the oscillations shift an extent phase or frequency modulated Wave telegraph 50 or angle proportional to the amplitude of the signalling systems are less subject to fading efapplied modulating frequencies. Phase modufects than systems known heretofore, the eflated oscillations are, however, less subject to fadciency of reception is greatly increased.

ing effects than frequency modulated oscillations. Numerous other objects of the present inven- Obviously, this method of signalling is of the tion, and advantages to be gained by the use thereof, will become apparent from the following detailed description thereof and therefrom when read in connection with the attached drawings, throughout which like reference characters indicate like parts, and in which:

Figure 1 illustrates diagrammatically the several units included in a transmitter arranged in accordance with the present invention; while,

Figure 2 shows the circuit arrangements of certain units of Figure 1 which are constructed in accordance with the present invention.

In Figure l, C indicates a phase or frequency modulating unit connected on the one hand to a source of constant high frequency oscillations D, which may include an output buffer stage, on the other hand to a frequency doubler E or several frequency doubles in cascade which may feed an antenna system by way of an amplifier and frequency multiplier F. The high frequency oscillations produced in D are supplied to C Where they are caused to be modulated in phase or frequency by an amplitude modulating stage B, which is supplied with either low frequency modulating oscillations or with voice frequency potentials from a source A. The frequency multiplier or multipliers in E may be of any type known today, and, since this unit forms no part of the present invention, description thereof is thought unnecessary at this point. The same remarks apply to the frequency multiplier and/or amplifier F and the radiating system connected therewith.

The oscillation generator D may be of any type so long as the oscillations produced thereby are constant in frequency and of constant amplitude. This oscillator preferably is of the long line frequency control type or of the crystal control type. The oscillator D may include a buffer output or, if it does not include a buffer output, a buffer output may be interposed between the oscillator D and the phase or frequency modulator C if necessary.

The phase modulator C comprises means including thermionic repeater tubes in which the oscillations generated at D are repeated and varied in phase or frequency in a manner characteristic of the voice frequency potentials or the modulating frequency oscillations supplied from A by way of B.

The unit B includes thermionic repeaters or amplitude modulators by means of which the low frequency oscillations or audio frequency potentials originating in A are utilized in a novel manner to impress on the high frequency oscillations repeated in C characteristic phase or frequency modulations. The unit B includes also the grid biasing filter network and the grid biasing potentiometers necessary to supply biasing potentials to the units A, B and C. rIhis filter network and potentiometer system is connected to a source I of direct current potentials. The unit B also includes the alternating current transformers necessary to supply filament current to the tubes in the units B and C.

The unit A includes a thermionic tube and novel circuits cooperating therewith in such a manner that the tube may function as a low frequency oscillation generator or as a Voice frequency amplifier merely by a single movement of a switch cooperating with the circuits of the tube. The unit A also includes the audio frequency transformer necessary to impress voice frequencies from the source 2 on to the thermionic tube therein when the latter is to be used as a voice frequency amplifier.

Alternating current for the thermionic tubes in the units A, B, and C is supplied from an alternating current source 3 connected by way of leads to the unit A, which is in turn connected by leads to the unit B, in which the filament transformers are included. The filament transformers in B are connected by filtered leads to the thermionic tubes in the unit C.

The necessary plate voltages for the thermionic tubes of the units A, B, and C are supplied from a direct current potential source l by way of a unit G, which includes filtering means for the direct current potentials, and a potentiometer arrangement whereby the proper voltages may be supplied to the different thermionic tubes.

The manner in which phase or frequency modulations are impressed on the carrier will now be described. Reference will first be made to the unit C of Figure 2. A pair of therrnionic repeaters K and L, of the screen grid type, have their control electrodes G and connected through leads to a blocking condenser IO, which is in turn connected with any source of constant high frequency oscillations, as, for example, the source D. Oscillations from the source D are impressed by way of condenser I@ on to the electrodes E and 'I substantially cophasally. The relative phase of these oscillations is shifted, however, since the oscillations reaching the grid 'l pass through a phase advancing means in the form of a variable condenser II, while the high frequency oscillations reaching the grid 6 pass through a phase retarding means in the form of an inductance I2.

The anode electrodes I3 and I Il are connected together and to the terminal of a tank circuit E5 which includes an inductance I and a variable capacity I6. The tank circuit i5 is tuned to resonance at the frequency of the oscillations supplied from D. The high frequency oscillations, slightly shifted in phase,and impressed on to the control electrodes 6 and 1, are repeated and amplified in the tubes K and L, and the energy from K and L appears in the tank circuit I5 shifted in phase an amount determined by the phase shift impressed on the energy by the elements I2 and II. This energy may be supplied from the tank circuit to the radiating system by way of the units E and F through a direct current blocking condenser I1. Anode potential for the tank circuit I5 is supplied by way of a lead I8 from a potentiometer P included in the unit G and supplied with energy from the source by way of filter circuit FC.

Energy for the filaments of the tubes K and L is supplied by leads I9 and 20 respectively from the secondary windings of transformers 'I' and 'Il respectively included in the unit B and supplied by way of leads 2| from the source 3 connected with unit A. In order that the amount of low frequency hum impressed on the thermionic repeaters K and L from the filament energizing source may be held at a minimum, the filament circuits thereof include hum filtering means in the form of resistances r and 1" connected in parallel with the filaments of tubes K and L respectively, said resistances being tapped at the electrical center and connected by way of space current indicating meters MA and by-pass condensers C to ground GL. The resistances r and r also form a low impedance path to ground for the low frequencies appearing in the input or output circuits. The low frequencies are in this manner shunted around the high impedance of the filament transformer windings, and lay-pass condensers C"-C l A low impedance path for the high frequency oscillations repeated in K and L is provided by by-passing condensers C' connected, as shown, in series across the terminals of the filaments cf each tube and having their electrical center connected, as shown, to ground GL. Volltmeter V, shunted by by-pass condensers C', may be connected across the terminals of the filament to indicate the voltage applied thereto. Normal direct current biasing potentials for the control electrodes l and I of tubes K and L is supplied by way of resistances R1, Rz from lead 22l connected to a movable point on a potentiometer resistance P1 associated with a filtering circuit F"C comprising choking inductances and parallel condensers and connected with the direct current biasing source l. The current drawn by the control electrodes tl and 'l of tubes K and L may be indicated by meters M'A inserted in the biasing current paths between 22 and the terminals of P and P and shunted by by-pass condensers C'. 'Ihe direct current biasing potential applied to the control electrodes is indicated by a voltmeter V1.

Applicant has now described the manner in which the high frequency oscillations originating in D are applied shifted in phase, but in a sense cophasally, to the control electrodes of the tubes K and L, amplified and repeated therein, and transferred therefrom substantially in phase to the tank circuit I5, from which they may be utilized.

The manner in which these oscillations are modulated in phase or frequency at signal frequency will now be pointed out.

In the present embodiment of the invention, the modulation is accomplished by impressing the modulating frequencies in phase opposition on the screen grid electrodes 24 and 25 of tubes K and L respectively by way of shielded leads 26 and 2l connected, as shown, to the anodes. 28 and 29 of thermionic tubes M and N respectively. The manner in which the modulating potentials are caused to appear at the terminals of leads '26 and 21 will be described hereinafter.

The effect of said potentials being applied in phase opposition to the screen grid electrodes 24 and 25, and the manner in which said signal oscillations are applied thereto in opposition, modulated in phase or frequency, and the high frequency oscillations repeated therein, will be set forth now,

Assume that no modulating frequencies are applied to the screen grid electrodes o-f tubes K and L. The same direct current biasing potential is supplied to the control electrodes, and the high frequency oscillations impressed on the control electrodes are substantially in phase, being shifted only in different senses by the impedances of the inductance I2 and capacity I I. The anode circuit of tube K Will supply, therefore, to the tank circuit, energy equal in amount to the energy supplied to the tank circuit I from the anode of tube L, The energies from these tubes will be of different phase and the energy supplied from the tank circuit to the frequency doubler or next stage will have a resultant phase determined by the phase of the separate energies supplied from the tubes K and L so that in this case the carrier oscillations will have no change or shift in phase.

The energy supplied to the tank circuit I5, from the tube which has the highest modulating potential applied to the screen grid electrode,

will be greater in amplitude than the energy supplied to the tank circuit I5 from the tube having a lesser modulating` potential applied to its screen grid. This is due to the fact that the effective potential applied to the screen grid of a screen gri-d tube governs the internal impedance of the tube, the amplification factor thereof, and other characteristics. Each of these variables in turn eiect the amount of energy supplied to the anode circuit of the tube. Therefore, varying in phase opposition the effective potentials of the screen grid electrodes of the tubes K and L, by modulati-ng potentials from the lines 255 and 2'I, varies the amount of energysaid tubes will supply to the tank circuit` I5.

The maximum possible phase deviation of the carrier is determined by the adjustment of impedances II and I2 of the grid phase shifting circuits. The phase shift, therefore, of the resul-tant energy in the tank circuit I5, is limited by the adjustments applied to the phase shifting circuits. The frequency of the phase deviation of the carrier is determined by the modulating frequency. The amount of phase deviation of the carrier is determined by the amplitude of the modulating frequency and is proportional to the amplitude of the modulating frequency. The amount of phase shift or deviation of the carrier or the tank circuit oscillations may, accordingly, be limited by the adjustments of the phase shifting circuits connected with the input of thev tubes. The amount of phase shift or deviation of the carrier or the tank circuit oscillations is determi-ned by the amount or difference of power delivered by one tube over the power delivered by the otherV tube, and by the phase difference of the energy delivered by both tubes. In other Words, the phase shift of the oscillations in the tank circuit I5 is the result of the increase of energy delivered by one tube while the energy delivered by the other tube decreases a like amount because of the phase difference in the alternating current energy delivered by each tube, and is proportional to said increase and decrease.

The phase shifts which take place, as indicated above, will be multiplied or increased by a frequency multiplier in case the oscillations from the tank circuit I5 are fed by way of a frequency multiplier or multipliers to the utilization circuit.

As pointed out briefly hereinbefore, one of the novel features of applicants invention resides in the means for supplying, by the use of a single tube, either low frequency oscillations or amplifled voice frequency potentials to the unit B, wherein they are utilized to apply in phase opposition the modulating potentials tothe screen grid electrodes of the phase modulator C by way of leads 26 and 2l.

YI'he low frequency oscillation generator or amplifier comprises a thermionic tube X having a cathode 3i), control electrode Si, and anode 32. When the tube is to be used as a low frequency oscillations generator the movable blades of the switch 34 are moved to the left and th-e control electrode 3I is connected by way of parasitic prevention resistor 33, switch 34, and lead 35 including blocking con-denser 36, to one terminal of an inductance 3l, the other terminal of which is ccnnected by way of lead 33 and switch 3d to lead 39, which is connected to the anode 32. The direct current grid bias circuit is completed by way of a grid leak resistance id connected between one terminal of the condenser 35 and ground, which is the same as connecting the grid 3l to the ground by way of resistance 40. The voltage drop across grid leak resistor 40, caused by the rectified grid current passing through it, supplies grid bias voltage to the grid of tube X when it acts as an oscillation generator. The direct current anode circuit which furnishes the charging potential to the anode 32 is completed by a lead 4| connected to a movable point on the inductance 31 and passing by way of switch 34, resistance 42, and current indicating device MZAZ to a point on the potentiometer resistance P. This point on P is moved to a position at which charging potentials, of a Value such that suiciently strong oscillations are produced in the tube X, are applied to the anode of the tube. The meter l\/i2A2 in the lead 4| permits checking of the direct current flowing in the anode circuit of tube X when it acts as an oscillator. The filament 30 of tube X is supplied with alternating current from the secondary winding of a transformer T2, the primary winding of which is connected with the line 2|.

When the electrodes of the tube X are energized, sustained oscillations are produced in the circuit including the inductance 31 and capacitors TC which are coupled between the anode 32 and control electrode in a well known manner. The frequency of these oscillations generated is determined by the amount of capacity connected in parallel with the adjustable inductance 31. The amount of capacity connected in parallel with the inductance 31 may be changed in predetermined increments by connecting one or more of the circuit tuning condensers TC in parallel with the inductance 31 by closing one or more of the keys S, S1, S2 and S3. The oscillations produced in the anode grid circuit of tube X are short-circuited around the anode potential source and associated resistances by a pair of by-pass condensers C connected, as shown, between the lead 4| and the two leads 43 between the lament 39 and the secondary winding of the transformer T2. In order to prevent any hum at the lament energizing current frequency from occurring in the tube X and associated anode circuit, and also to act as a by-pass to ground for low frequency current, the electrical center of the balancing resistance r2 is connected to ground GL. The low frequency alternating current potentials developed in the tank circuit including the inductance 31 and the selected tuning condenser TC are supplied by way of coupling condenser 44 to the terminal of a potentiometer resistance 45, the other terminal of which is connected directly to ground GL, thereby supplying a potentiometer load circuit.

These potential variations at the frequency determined by the oscillation circuit 31, TC, are fed by way of leads 46 from potentiometer 45 and switch 34 to a line 41 which terminates in the primary winding of a modulation frequency transformer MT, from which they may be utilized to act through the unit B to modulate in frequency or in phase the oscillations from unit D repeated in the unit C in a manner which will be pointed out hereinafter. In order that the amplitude of these modulations may be adjustable or varied, one of the leads 46 is connected to a movable point on the resistance 45, as shown. Most of the oscillations which appear in the direct current charging circuit 4|, are filtered out by way of a by-pass condenser C connecting one terminal of the resistance 42 to ground.

In the description of the unit A, given above, it was assumed that low frequency oscillations were to be developed therein and impressed on the unit B, from which they were to cause frequency or phase modulation in the oscillations repeated in C. It will now be assumed that instead of modulating with low frequency oscillations other audio frequency potentials, as, for example, voice frequencies, are to be used to modulate the carrier repeated in C and, further, that the tube X of the unit A is to amplify these potentials or voice frequencies before they are fed to the unit B to be used to modulate the high frequency energy repeated in C. To use the tube X as an amplifier the blades of the multiple switch 34 are moved into a right hand position to close the circuits associated with the right hand row of contacts. In this position the grid electrode 3| of tube X is connected through switch 34 in series with the secondary winding of a transformer T3 and by way of lead 48 to a point on a resistance P2 connected in parallel with the filter FC' which is energized from the direct current source I. The connection 48 supplies direct current biasing potential to the grid electrode 3| by way of parasitic prevention resistance 33 to charge the grid to a point at which the tube X operates as a good linear amplifier. The transformer T3 has its primary winding connected in parallel with a potentiometer resistance 49, which is connected by way of leads 5U and jack 5| to the source of audio frequency oscillations 2.

In order that the amplitude or magnitude of the audio frequency oscillations applied to the primary winding of transformer T3 may be adjustable, one of the leads 50 is connected to a movable point on resistance 49. The input circuit for the modulating frequencies impressed on to the secondary winding of the transformer Ta is completed by way of an audio frequency bypassing condenser C connecting the low potential terminal of the secondary winding of T3 to ground GL and to the electrical center of the cathode 3E). In this manner modulating frequencies from the source are impressed upon the input circuit of the tube A for amplification. The modulating potentials or currents amplified in the tube X appear on the anode 32 and are fed by way of lead 39 and switch 34, and one of the pair of leads 41, to the primary winding of transformer MT, and from the primary winding of transformer MT by way of the other lead of the pair of leads 41, switch 34, resistance 42, current indicating means M2A2, and lead 4| to the movable point on the potentiometer resistance P. In this manner a charging potential is applied to the anode of tube X in the same manner in which it was applied when the tube X was used as an oscillations generator. The alternating current anode circuit is completed by way of audio frequency by-pass condenser Ca connected between one of the leads 41 and ground and cathode 39. Condenser C' prevents oscillations appearing in this anode circuit from being transferred by way of lead 4| to the resistance P to modulate therein any other oscillations which may appear from the other units. Further and more complete filtering of this circuit is insured by a by-pass condenser C connected between one terminal of resistance 42 and ground GL.

The modulating frequencies appearing in the source 2 are impressed by way of transformer T3 on to the input electrodes of tube X, are repeated and amplified therein, and are impressed on the primary winding of the transformer MT for a purpose which will appear hereinafter.

Any radio frequency oscillations appearing in the lines 50 from source 2 are prevented from reaching the transformer T3 by means of radio frequency by-pass condensers 52 and 54 connected as shown. Condenser 53, connected in series with the primary winding of transformer Ta, prevents any direct current from source 2 from reaching said Winding and also acts as an impedance to reduce the volume of the low frequency voice currents which are normally overemphasized in an audio frequency transformer.

The manner in which the oscillations at modulating frequency appearing in the primary Winding of the transformer MT in the unit B, Whether they originate in the tube X, acting as an oscillation generator, or originate in the' source 2 and are amplified in X, are utilized. by the unit B to produce frequency or phase modulation of the carrier repeated in the unit C Will now be described.

TWO thermionic tubes M and N have their control electrodes 6i] and tl respectively connected by Way of parasitic prevention resistances 62 and iid respectively and normally closed contacts of the jack 64 and leads 65 to the opposite terminals of the secondary Winding of transformer MT. In this manner modulating fre-` quencies or voltages are applied in opposition to the control electrodes of tubes M and N. Equal direct current biasing potentials for the control electrodes Gil and 6I are supplied by way of a lead t6 connected on the one hand to a movable point on the resistance P4 connected in parallel With the filter circuit FC supplied with energy u from the source l, and on the other hand through a current indicating device M3A3 to the electrical center of the secondary winding of the transformer MT, from which Winding it is applied by Way of leads 65 and jacks 64 to the control electrodes iii] and Si. The filaments 61 and 68 of tubes M and N are supplied With alternating heating current over lines 69 connected with the secondary Winding of a transformer T4, the prie mary Winding of which is connected With the supply leads 2|.

The thermionic tubes M and N are balanced with respect to the oscillations in the filament heating circuit by connecting the electrical midpoint of balancing resistances r3 and r4 connected across the cathodes 6l and 68 respectively to ground GL. These resistances r3 and r4 furnish low impedance by-pass paths around trans= former T4 to ground for loW frequency oscilla; tions. These resistances also tend to prevent any hum at the frequency of the energizing source from being developed.

The modulating potentials impressed in oppo= sition from the transformer MT to the control electrodes of the tubes M and N are repeated in inverse sense and amplified therein and ap= pear in phase opposition on the anode electrodes 28 and 29 thereof respectively. The direct current anode circuit of tube M is completed by Way of a current indicating device M4A4, lead 2li, resistance it, and lead 4| to a point on the resistance P connected in parallel With the filtering circuit FC supplied from the high voltage source li. The anode direct current circuit of the tube N is completed by Way of current indieating device M4A'4, lead 2l, resistance' 1|, and lead di to a point on the resistance P`. Most of the audio and substantially all of the higher potential oscillations are by-passed around the anode direct current energizing source by Way of a by-pass condenser C connected between the terminals of the resistances 1U and TI and the ground GL.l In some cases the resistances and 'H may be replaced by choke coils. However, in most cases the resistance gives the more desirable Wave form and is, accordingly, used.

The conductivity of the tubes M and N depends upon the effective potential applied to the control electrodes thereof. The effective potential applied to the control electrodes of the tubes M and N depends upon the constant direct current potential and the modulating potentials applied adding or in opposition thereto. The current which flows in the anode circuits of the tubes M and N is determined by the conductivity of the tubes.r It therefore follows that the amount of current which iioWs in the anode circuits of tubes M and N varies at modulating frequency and depends upon the amplitude of the modulating frequency. Since the current flowing in the anode circuits of tubes M and N respectively varies at modulating frequency, the potential drop through resistances l0 and 'll also vari-es at modulating frequency. This potential drop through 10 and 'Il being in negative sense to the potential supplied by line 4| from P is applied directly by Way of leads 2l and 26 respectively to the screen grid electrodes 25 and 24 of tubes L and K respectively. As pointed out hereinbefore, the effective voltage on the screen grid electrodes of the repeater tubes K and L determines the conductivityv of said tubes and therefore determines the amount of current the respective tubes supply to the tank circuit l5. Obviously, the potential variations at signal frequency, applied from the terminals of resistances lll and 'H through lines 26 and 2l modulate in C the carrier frequency energy repeated in tubes K and L supplied from the source D. As pointed out before tliecarrier frequency supplied to the grids 24 and 25 of tubes K and L is of equal amplitude by shifting oppositely an equal amount in phase so that the carrier frequency repeated by tubes K- and L is also shifted oppositely but equally in phase. However, as the sig-v rial varies, tubes K and L have their screen grid potentials varied in phase opposition and consequently the amplitude of the carrier output cnergy of these tubes is varied or modulated according to the signal. But since the anodes I3 and I4 of tubes K and L are connected in parallel to the same point on tank circuit I5, the amplitude modulation cancels and disappears but phase modulation will appear. The phase of the oscillations in tank circuit I5 Will approach that of the tube supplying the most carrier energy. This phase shift of the oscillations in' the tank circuit l5 will be proportional to the amount of energy supplied by one tube over that supplied by the other. The degree of phase deviation will be proportional to the intensity or amplitude of the signal and the frequency of phase shift will be the signal frequency.

Alternating current for the laments of all of the tubes in each of the units A, B, and C is supplied from a source 3 by Way of protection devices PO and lines 2l. The amplitude of this current may be determinedby the variable resistance VR connected in series With one side of the line 2l. Any oscillations which have not been bypassed to ground by the by-pass condensers described hereinbefore are shunted around the source 3 by by-pass condensers C connecting each side of the line 14 to ground GL.

To further insure that the oscillations, etc., developed and Worked with in the several units,

CII

are confined to said units, the leads, such as 4| and the leads between the transformers T and T1 and the laments of the tubes energized thereby, are iiltered by way of by-pass condensers C connected as shown between said leads and ground GL. In a like manner the corresponding leads, Where they enter the unit C after passing from the units B and G, are again ltered by means of by-pass condensers C', there being a by-pass condenser connected between each line and the ground GL.

In practice it is important that the tubes M and N of the unit B impart to the modulating frequency the same amplification or are otherwise balanced in such a manner that the potentials appearing at the terminals of resistances 'l0 and 'il are similar in amplitude in order that the proper phase or frequency modulation is impressed on the carrier.

In order that the effect of tubes M and N on the modulating frequency may be determined and regulated, a jack 64 is connected, as brieiiy described hereinbefore, in the input circuit thereof in order that a monitoring circuit may be utilized to check on the modulating characteristics of this unit. The monitoring circuit forms no part of the present invention and will not be described herein.

The above description, and the drawings referred to therein, have been given merely for purposes of illustration since, obviously, many changes may be made therein without departing from the scope of the present invention. For example, different types tubes could be used in the unit A wherein the modulating frequency oscillations are developed or the modulating potentials energized and, likewise, many changes could be made in the circuit thereof. In a like manner, different type tubes, arranged in different circuits, could be used in the unit B. Furthermore, it is clearly understood that other tubes than those shown might be used in place of the thermionic tubes in the unit C and that likewise the circuits in which said tubes are connected may be departed from materially, without departing from the scope of the present invention.

Having thus described my invention and the operation thereof, what I claim is:

1. Means for producing phase modulated oscillations comprising, high frequency oscillation generating means, repeating means including a pair of electron discharge tubes each having, an anode, a cathode, and a control electrode, means for connecting the anodes of said tubes in parallel, means for applying oscillations from said generating means in phase displaced relation to the control electrodes of said discharge tubes, a thermionic device having an anode, a cathode and a control grid, a circuit resonant at modulating potential frequency, a source of modulating potentials, switching means for connecting said resonant circuit between the anode and control grid and cathode of said device to produce oscillations, or the control grid and cathode of said device to said source of modulating potentials to act as an amplifier of the modulating potentials, and means connected between the anode of said last named device and said repeaters to vary in opposite directions the operating characteristics of said repeaters.

2. A device for producing phase or frequency modulated waves comprising, the combination of a carrier wave generator, a low frequency oscillator and a source of voice frequency potentials,

a phase modulator havingY its input circuits connected to said carrier wave generator, a frequency multiplier connected to the output of said phase modulator, a load circuit coupled to said frequency multiplier and switching Imeans for connecting said low frequency oscillator to said phase modulator to transmit phase or frequency wobbled waves to said load circuit or to connect said voice frequency potential source to said phase modulator to transmit telephony modulated waves to said load circuit.

3. A device for producing phase or frequency modulated waves comprising, the combination of a carrier wave generator, a phase modulator having its input electrodes coupled to said carrier wave generator, an audio frequency amplifier connected with electrodes of said phase modulator, a phase and frequency multiplier coupled With the output electrodes of said phase modulator, a radio frequency amplitude increaser coupled with the output of said phase and frequency multiplier, a load circuit coupled with the output of said last named amplitude increaser, a source of signals, a source of low frequency oscillations, and circuits for impressing signals from said first source on said audio frequency amplifier to transmit wave energy modulated in phase or frequency in accordance with said signals from said transmitter or for impressing oscillations from said second source on said audio frequency amplifier to transmit Waves wobbled in phase or frequency in accordance with said low frequency oscillations from said transmitter.

4. A device for phase or frequency modulating a carrier wave by telegraphy or telephony signals comprising, the combination of a low frequency oscillator and a source of voice frequency potentials, a phase modulator having its input energized by said carrier wave, a frequency multiplier connected to the output of said phase modulator, a load circuit coupled to said frequency multiplier and means for connecting said low frequency oscillator to said phase modulator to transmit telegraphy signals to said load circuit or to connect said voice frequency potential source to said phase modulator to transmit telephony signals to said load circuit.

5. A device for phase or frequency modulating a carrier Wave by telephony or telegraphy signals comprising, the combination of an audio frequency amplifier, a phase modulator having its input electrodes energized by said carrier wave energy, an audio frequency amplifier connected with electrodes of said phase modulator, a phase and frequency multiplier coupled with the output electrodes of said phase modulator, a radio frequency amplitude increaser coupled with the output of said phase and frequency multiplier, a radiating circuit coupled with said last named amplitude increaser, a source of voice frequency signals, a source of low frequency oscillations, and means for impressing signals from said first sourceon said audio frequency amplifier to transmit telephony signals modulated in phase or frequency in accordance with said signals from said first source from said transmitter or for impressing low frequency oscillations from said second source on said audio frequency amplifier to transmit wave energy modulated in phase or frequency in accordance with said low frequency oscillations from said transmitter for telegraphy signaling.

6. In a phase modulator, a pair of thermionic tubes each having an anode, a cathode, a control electrode and anauxiliary electrode, a circuit including an inductance connected to the control electrode of one of said tubes, a circuit including a condenser connected to the control electrode of the other of said tubes, means for applying high frequency oscillations in phase to said circuits to thereby energize the control electrodes of said tubes by phase displaced oscillations of like frequency, an output circuit connecting the anodes of said tubes in parallel, a source of modulating potentials, an impedance, a circuit connecting said source of modulating potentials to said impedance for impressing said modulating potentials across said impedance, a circuit connecting a point on said impedance to the cathode of said tube, and circuits connecting points on said impedance at Which said modulating potentials are of unlike phase to the auxiliary electrodes of said tubes, thereby varying in unlike manner the conductivity of said tubes in accordance with potential variations in said impedance.

7. In a telegraphy or telephony signalling systern, a circuit tuned to oscillate when energized at a modulation frequency rate, a source of voice frequency potentials, a thermionc device having input and output electrodes, a pair of therrnionic tubes each having input electrodes, means for applying high frequency oscillations of like frequency but displaced in phase to the input electrodes of said pair of tubes, an impedance, a circuit connecting said impedance to the output electrodes of said device, whereby potentials are impressed from said device onto said impedance when the input electrodes of said device are energized, circuits connecting different points on said impedance tolike electrodes in said pair of tubes to apply modulating potentials in phase opposition to said like electrodes in said tubes, and a multiple switch and contacts cooperating with said source of voice frequency potentials to couple the same to the input electrodes of said device in one position of said switch when it is desired to signal by telephony, said switch cooperating with said resonant circuit to couple the same to the input electrodes of said device to produce oscillations in said tuned circuit in another position of said switch when it is desired to send telegraphy signals.

GEORGE L. USSELMAN.

Cil 

